As more people get vaccinated, we're starting to learn more about rare instances of breakthrough cases.
These are people who get sick or infected despite being vaccinated.
Understanding how these infections occur can help you protect yourself and your family.
During spring break, University of Chicago freshman Chelsea Seifer received her first dose of the Moderna vaccine. When she returned to campus, she ate with her usual group of friends.
A few days later, she started feeling ill and tested positive for COVID-19.
"The reason that there is an outbreak on campus right now is more so because of spring break than it is anything else," she said.
She is quarantining along with dozens of other COVID-positive students.
"I would say most people in here have gotten their first shot," Seifer said.
Dr. Hector Flores with Adventist Health White Memorial tells his vaccinated patients to continue masking and staying apart when not at home
"It takes about two weeks after the first shot for any immunity to begin to present itself," he said.
Flores said even with both doses, any exposure can still pose a danger.
"We've seen some reports of what are called breakthrough infections where somebody has been fully immunized, and they still get infection," he said. "What we suspect is that there may be a potential for someone who's fully vaccinated to carry the virus to someone who hasn't been vaccinated."
Still, Flores said the vaccine protects against severe illness. Breakthrough cases give scientists a chance to understand what needs to be done to lengthen immunity and protect against variants.
"What we expect is that there's probably going to be a need for a booster either annually or periodically," he said.
In quarantine, Seifer can't have outside food or visitors. Studying has been difficult.
She said, "I have to go on my computer several hours a day and it's significantly harder when you have COVID."
Seifer now knows even with the vaccine, she's not invincible.
"Do as I say not as I do. Because you're not immune and being 18 does not mean that you're built different or stronger than this thing because I certainly am not," she said.